The present invention is aimed specifically at remedying these drawbacks, and in particular at providing a process for tracking and/or monitoring the operation of a near-infrared spectrometer and the manufacturing unit to which it is linked.
By virtue of this process it is possible to expose disturbances, drifting, anomalies of operation of the spectrometer and of the associated measurement rig as well as of the manufacturing unit to which it is linked, to identify the causes of these malfunctions and to make provisions suitable for each situation: for example to declare the result of an analysis invalid and to warn the operator running the unit to which the spectrometer is linked and to supply him with elements for making his decisions.
This process finds its application in analysis laboratories and the manufacturing units of the chemical, petroleum, pharmaceutical, cosmetological and agro-food industries.
For this purpose the present invention proposes a process for tracking and monitoring by means of at least one indicator, the operation of a unit for manufacturing a product and/or a near-infrared spectrometer fed with the said product, the said spectrometer delivering spectra consisting of series of values of absorbance for various values of wavelengths, consisting in executing the following steps:
periodically recording, in the form of numerical data, spectra arising from the near-infrared spectrometer, PA1 mathematically transforming the numerical data of each recorded spectrum so as to obtain transformed spectra, PA1 constructing a string of work spectra from the values obtained previously, by selecting from each transformed spectrum, a set of consecutive wavelengths characteristic of the manufactured product, characterized in that it consists in executing the following steps also: PA1 choosing from the first work spectrum a number 1 of consecutive wavelengths, PA1 computing coefficients by series decomposition of the first spectrum, PA1 choosing the first p coefficients, PA1 determining a first recomposed spectrum by recomposing the first work spectrum from the first p coefficients, PA1 computing a parameter STDm through the formula: EQU STDm=[.SIGMA..sub.i (A.sub.i -A'.sub.i).sup.2 /l].sup.1/2 PA1 in which: PA1 iteratively repeating the computation of the parameter STDm with the first p+q coefficients, q going from 1 to l/4, PA1 comparing the values STDm thus obtained with a threshold value STDs, PA1 adopting the number n of coefficients corresponding to the value STDm immediately greater than the value STDs. PA1 STD represents the indicator of proper operation, PA1 A.sub.j represents the mathematically transformed absorbance value for wavelength j of each work spectrum, PA1 A'.sub.j represents the mathematically transformed absorbance value for wavelength j of each work spectrum recomposed with the adopted number n of coefficients, PA1 j varies from 1 to l PA1 l represents the chosen number of wavelengths.
computing coefficients by series decomposition of each work spectrum, PA2 choosing a limited number n of coefficients by performing a selection procedure, PA2 determining a recomposed spectrum by recomposing each work spectrum from the chosen coefficients, PA2 computing at least one indicator of proper operation of the manufacturing unit and/or of the near-infrared spectrometer, by means of a mathematical expression which combines the values of each work spectrum and those of the corresponding recomposed spectrum, PA2 tracking the evolution over time of the indicator of proper operation. PA2 A.sub.i represents the mathematically transformed absorbance value for wavelength i of the first work spectrum, PA2 A'.sub.i represents the mathematically transformed absorbance value for wavelength i of the first recomposed work spectrum, PA2 i varies from 1 to l, PA2 l represents the chosen number of wavelengths
According to another characteristic of the process of the invention the decomposition of the work spectra is performed by means of a series decomposition chosen from Fourier and Hadamard series and wavelet series decompositions.
According to another characteristic of the process of the invention with the string of work spectra including a first spectrum, the selection procedure consists in determining the number n of coefficients by executing the following steps:
According to another characteristic of the process of the invention the near-infrared spectrometer having known repeatability, the threshold value STDs is chosen equal to the standard deviation of the said repeatability.
According to another characteristic of the process of the invention the mathematical expression which combines the values of the transformed spectrum and those of the recomposed spectrum is the following: EQU STD=[.SIGMA..sub.j (A.sub.j -A'.sub.j).sup.2 /l].sup.1/2
in which:
According to another characteristic of the process of the invention in order to track the evolution over time of the indicator of proper operation, a monovariate control chart is used.
According to another characteristic of the process of the invention, a causes/effects diagram is used to track the evolution over time of the indicator of proper operation.